Taglesson stages

To begin with, I am not aware of any reliable statistics.  I can only draw on my personal experience and summarize a number of related Google search results. It is obvious, I hope, that it is impossible to spend more than 3 clock hours talking without a break.  I guess that’s the maximum.  As for the minimum, an online lesson can be as long as a regular phone call, i.e. it can last for as...